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Quantifying the Amount of Spine in Fly Rods

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gordonjudd
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Re: Quantifying the Amount of Spine in Fly Rods

#21

Post by gordonjudd »

If this topic has any relevance to rod making then I would think that coming up with an answer to these questions
That brings up an interesting question as to the guide placement relative to the strong FLO plane.

If you wanted to reduce the spine would you put the guides on the strong FLO plane of the blank or its weak FLO plane?

That same question applies to aligning the spine in a four piece rod. How would you align the strong FLO axis of the upper sections to the strong FLO axis of the butt to minimize the overall spine in the rod?
should be of interest.

What are your thoughts on those questions? Note this applies to just the configuration of the dynamic spine or FLO planes. Any blank curvature will have a big effect on the static spine alignment which can best be found with a spine finder.

I think that Tutleman has explained the reason why the static and dynamic splines are rarely aligned is because of blank curvature. That is the answer to the question raised in this topic on the old board.

Gordy
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Merlin
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Re: Quantifying the Amount of Spine in Fly Rods

#22

Post by Merlin »

Gordy

The effect of guides on spine is hard to evaluate, if it can be. A spine can rotate around a rod section and no one will rotate the guides to follow.

The important FLO is the one of the butt as demonstrated by Graig Spolek, and you can rotate NBPs of other sections to minimize bending assymetry which is important to avoid lateral deviation of the tip.

No builder uses a FLO testing device for that, as far as I know.

Merlin
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Re: Quantifying the Amount of Spine in Fly Rods

#23

Post by gordonjudd »

The effect of guides on spine is hard to evaluate, if it can be.
Merlin,
I agree that analyzing the overall effect of varying scrim overlap on a rod section would be difficult if not impossible since the only way to know how much overlap there was at a given point in the rod would be to cut through different cross-sections as Dr. Spolek did in his spline paper.
Image

That is why Tutleman (and I for that matter) find it amazing that something as complicated as spine can be accurately modeled with a simple quadrature spring model.
The important FLO is the one of the butt as demonstrated by Graig Spolek, and you can rotate NBPs of other sections to minimize bending assymetry which is important to avoid lateral deviation of the tip.
And I think that Tutleman's FLO approach provides a way of doing such a dynamic spine alignment in a straight forward manner.

I would start the process by aligning the weak FLO plane vertically. Then I would align the other sections with their strong FlO plane oriented horizontally. Thus the weak spring constant of the butt section would be added to the strong spring constant planes of the upper sections. That would tend to minimize the different of the spring constants in the overall rod and thus reduce the net spine of the rod.

I still would not want the rod to twist when fighting a fish so at that point I would put the dynamically aligned section in a static spine finder, add a significant mass to the tip and let the rod spin to its static neutral bending plane (NPB). I would expect that unless the rod had severe curvature the amount of that spin to the NBP would be relatively small since you started with the stronger butt section aligned to its weak FLO plane. Then I would put the guides on the bottom of that NBP plane.

If the guides add much stiffening (and Spolek thinks the amount of stiffening would be insignificant) they would be one the weak FLO plane of the butt and the strong FLO plane of the upper sections. Thus any stiffening they added would further reduce the overall spine in the rod, and yet you would have no twist when fighting a strong fish.

I am not convinced tip whirl is a problem since the tip will tend to follow the pull from the line but the above approach should minimize it.

Tutleman is adamant that spine finders should not be used to properly align golf clubs. As he says (and his comments would also apply to fly rod blanks)
What happens when there is both spine and residual bend? Unless the spine effects are large enough to overwhelm the residual bend, you will get spine and NBP directions that do not conform to the laws of phyics -- and therefore are wrong.

FLO finds the real spine and NBP, unpolluted by non-spine properties like residual bend.

Because conventional, bearing-based spine finders are not a reliable way to find a spine. They are thrown off by any residual bend in the shaft. If the shaft is very straight and has a lot of spine, then they will give the right answer. But, for most shafts, the residual bend is enough to partially mask a modest spine, and the spine-finder gives the wrong direction.
I would be interested to see if people are using a different approach to minizing the overall spine and rod twist when building a rod. I am a convert to Tulteman's FLO approach. With a high speed camera it is easy to measure the vibration frequency to find the strong and weak FLO planes then it just a matter of using the above approach to get a finished rod with the least amount of overall spine and rod twist.

Gordy
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Re: Quantifying the Amount of Spine in Fly Rods

#24

Post by Paul Arden »

Hi guys,

Very interesting discussion! It raises a question I have, are the weak planes of bending always 180 degrees apart? Or can they align closer to the spine? I assume if the spine curves down the blank then the “plane of bending” rotates around the rod according to load? Does ring positioning somehow create a new bending plane?

Sorry that’s three questions but I think partly relevant to this discussion? Since question 4 (!) is does this equally apply to the rod in question?

Thanks!!
Paul
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Re: Quantifying the Amount of Spine in Fly Rods

#25

Post by Merlin »

Hi Paul

Usually people consider spine as another way to describe natural bending planes (90 degrees apart from each other, the spine is perpendicular to the NBP). Real life can be different, spine (local stiffness) can be different from NBP. All situations can be found from no spine / bending assymetric to spine / bending neutral.

I do not think that guides can influence significantly spine or NBP, they may represent a very slight stiffness increase on tips, and nothing on butt and butt mid. And like Gordy said, the important FLO is in the butt section.

Merlin
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Re: Quantifying the Amount of Spine in Fly Rods

#26

Post by gordonjudd »

It raises a question I have, are the weak planes of bending always 180 degrees apart? Or can they align closer to the spine?
Paul,
That should be the case for a blank with little curvature. As Merlin noted the spine should have 180 degree symmetry where the weak and strong FLO planes are 90 degrees apart.

But as Tutleman notes here that is not the case with a curved blank.
That's a difference of 6mm, or 30% of the total 20mm bend. So the shaft is deflected more in one direction than the other direction. 30% more, in fact. The result: it will take 30% more force to deflect it. So there's a lot more force in one direction than the other. And that difference in force is how a feel finder locates the spine.

Because of the forces as you turn the shaft, you will come to the conclusion that there is a spine on one side and an NBP directly opposite. There are two things wrong with this conclusion:

We started out by saying the shaft has no spine, so the conclusion has to be wrong.
We know from physics that, if there is a spine in one direction, the opposite direction will have a spine, not an NBP. So the feel finder is telling us something that is physically impossible.

This explains what Bill Day calls a Type 1 shaft, a shaft with a single spine on one side and a single NBP opposite. It also explains why he says this is common in steel shafts. The vast majority of steel shafts have very little spine, so any residual bend will overwhelm what spine there is. The residual bend will be all that the feel finder can measure.
So if you have a blank where the weak and strong bending planes appear to be 180 degrees apart then you are measuring blank curvature not spine.
I assume if the spine curves down the blank then the “plane of bending” rotates around the rod according to load?
Certainly in a spine finder the angle for the NBP will vary slightly depending on the amount of tip load.

I would not be surprised to find that variation results from the effect that rod curvature has on the static spine angle. Same thing applies in making spring constant tests. The rod will appear to be weaker when the deflection is measured on the inside of the curvature as opposed to testing with the rod rotated 180 degrees so the initial tip position is above the position it has on the underside of the curvature.

That is why Tutleman recommends measuring the slope of the deflection vs tip load curve about some large deflection with a differential stiffness test since the relative effect of blank curvature will be much smaller for larger deflection. He says that careful differential deflection test should have a stiffness variation that matches up with the FLO angles.

I am not sure that FLO tests are affected by the magnitude of the tip swing. If you are on a FLO plane the tip will continue to track straight up and down until the vibrations die out to small values where you might start to see some whirling.

That is why the FLO tests are a much better way to find and measure spine than a spine finder. I have yet to see a blank with no spine or no curvature so you should use FLO test to get spine angles that are not impacted by blank curvature.

However I would still reserve the final guide placement to be on the inside of the curve produced with a large deflection in a spline finder.

Gordy
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Re: Quantifying the Amount of Spine in Fly Rods

#27

Post by gordonjudd »

No builder uses a FLO testing device for that, as far as I know.
Merlin,
I think that is true, and up to now neither have I since I only recently became aware of Tutleman's FLO approach to aligning golf shafts even though he wrote his articles in 2008.

Supposedly most fly rod manufacturers align the guides in order to get a rod that looks as straight as possible. Thus giving precedence to cosmetics over performance.

Others use spine finders (especially for big game rods) so the rod will not twist in the hands when fighting a strong Tuna or big game fish. Thus they consider the static fighting properties of a rod over it dynamic casting performance. That makes sense for a trolling rod, but maybe is missing something for a fly rod where its casting performace outweighs it's fish fighting performance.

I think the FLO approach will provide the best compromise in minimizing the ultimate spine of a finished rod while still providing a rod that doesn't twist in the hand when fighting a big fish.

Would you agree, or would you consider the added testing it takes to find the FLO axes not worth the additional effort?

I think my previous use of aligning the blank sections based on spine finder measurement was actually aligning for blank curvature, not spine, now that I understand Tutleman's FLO approach.

Gordy
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Re: Quantifying the Amount of Spine in Fly Rods

#28

Post by Paul Arden »

Thank you. So it should actually be quite easy to find the FLO with a laser pointer. I obviously need to try this! It does raise the issue that I always twist rings to different angles.

Cheers, Paul
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